docs(tt5): record macOS Tier-4 confirmation + Windows verification stance

- TT5: macOS is now fully covered — the full suite incl. Tier 4 ran green
  natively on macOS (4 flows + startup; Linux-only RSS test cfg-skipped).
- TT5 Windows wording: automated execution is the one open piece. A standing
  Windows CI runner is more involved than the Linux/macOS runners already in
  use; kept open with no timing promise. Interim: Windows builds ship every
  release and are verified by running the suite on Windows by hand periodically
  — the same builds, manually verified rather than per-push. TT5 stays [/] by
  deliberate scope. Framed in project terms, no host specifics.
- handoff-76 §6: macOS confirmation, the `pid` dead-code fix (1ffe11c), normal
  off-target crate downloads, and the Windows decision.

docs/requirements.md

@@ -938,14 +938,24 @@ since ADR-0027.)
   *(Partial, updated 2026-06-22. **CI is live** on the self-hosted
   Gitea Actions (`docs/ci/adr/`): the gate runs `clippy -D warnings`
   + `cargo test` (now Tiers **1–4** — the `e2e_pty` target runs by
-  default) on the **Linux** runner for every branch push / PR, and
-  `release-macos` runs the suite natively on the **macOS** runner.
-  **Tier 4 in CI on Linux is now met** (TT4); PTY-in-container was
-  validated (openpty + spawn under Docker), first real CI run is the
-  final confirmation. **Windows is build-only** — cross-compiled,
-  not executed (no Windows runner). "Stable Rust" is satisfied by
-  the flake's pinned `1.95.0`. **Remaining for full TT5: a Windows
-  execution runner** (the macOS + Tier-4 gaps are now closed).)*
+  default) on the **Linux** runner for every branch push / PR.
+  **macOS is fully covered**: `release-macos` runs the whole suite
+  natively on the macOS runner, and Tier 4 was confirmed green on
+  macOS (2026-06-22 — the 4 flows + startup; the Linux-only RSS probe
+  is `#[cfg]`-skipped). **Tier 4 in CI on Linux is met** (TT4);
+  PTY-in-container was validated (openpty + spawn under Docker), with
+  the first real gate run the final confirmation. "Stable Rust" is
+  satisfied by the flake's pinned `1.95.0`.
+  **Windows — automated execution is the one open piece.** Windows
+  binaries are first-class: cross-built and shipped for every release
+  (D1/D2), and we verify them by **running the suite on Windows by
+  hand from time to time** so the Windows experience stays sound
+  between releases. A standing Windows CI runner is more involved to
+  operate than the Linux and macOS runners already in use; we intend
+  to keep looking for a clean solution but make no promises on timing.
+  Until then, Windows users get exactly the same builds, verified
+  manually rather than on every push. So TT5 stays `[/]` by deliberate
+  scope, not neglect.)*
 
 ## Cross-cutting